Tach question

[gregsdrums]

The tachometer in my 72 midget does not work. All other gauges function properly. Would appreciate any suggestions...

 

[dklawson]

Did the tach ever work for you or is this a new occurrence?

I can't remember what year the tach type changed. Early electric tachs are marked "RVI" on their face. Later tachs will be marked "RVC".

The RVI tachs are called impulse tachs. Coil current passes through an inductive loop on (or inside) the tach. If you have an RVI tach, and it is hooked up properly but doesn't work, there are two possibilities. 1) The tach is dead (not surprising after 38 years), or 2) perhaps you have installed an electronic ignition (RVI tachs don't like electronic ignitions). A dead RVI tach can sometimes be revived by replacing one of the internal capacitors and/or the two transistors inside.

If you have a later RVC tach, those are voltage pulse sensing. They use a single wire connection to coil (-) to measure how many times a second the points open and close. If you have one of those that is hooked up correctly but not working, you may or may not be able to find the problem inside. Some of the later RVC tachs I have seen have very little on them that can be identified or replaced.

 

[gregsdrums]

Thanks for the reply. It's an RVI and the car was stored for years.

 

[spritenut]

Check the 2 white leads, the green lead, and the ground.
Might just be a dirty or loose connection.

 

[dklawson]

Agreed, do check the connections. However, it is not likely to be a problem with the white leads if the engine runs.